Ping plotting with PowerShell

Waaaay back we used to use a spiffy little tool called “ping plotter” to discover vacant IP addresses on our subnets. I had not had to do an exhaustive study of this for awhile. When it came up again today, I thought “I’ll bet we can do that with two lines of PowerShell.” But I was wrong… it took three lines, since I needed to initiate an array variable:

#Initialize $range as an array variable:
$range = @()

#Populate $range with integers from 2 though 254 
#  (for a Class C ipv4 subnet):
for ($i=2; $i -le 254; $i++) {$range += $i}

#Write out IP addresses for systems that do not have registered DNS 
#  names in the IP subnet 192.168.1.1/24:
$range | % {$ip = "192.168.1." + $_ ; $out = & nslookup $ip 2>&1; `
  if ($out -match 'Non-existent domain') {write-host $ip}}

Now some variations… write out only addresses with no DNS entry and that do not respond to ping. (This will help to weed out addresses that are in use that for whatever reason to not have a DNS name.):

$range | % {$ip = "132.198.102." + $_ ; $out = & nslookup $ip 2>&1; `
  if ($out -match 'Non-existent domain') {$out2 = & ping $ip -n 1; `
  if ($out2 -match 'Destination host unreachable') {write-host $ip}}}

… and perhaps most usefully, write out addresses with no DNS entry and that cannot be located using ARP. (This will weed out in use addresses with no DNS and a firewall that blocks ICMP packets.):

$range | % {$ip = "132.198.102." + $_ ; $out = & nslookup $ip 2>&1; `
  if ($out -match 'Non-existent domain') {& ping $ip -n 1 > $null; `
  $out2 = arp -a $ip; if ($out2 -match 'No ARP Entries') {write-host $ip}}}
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